This invention relates to microswitches and, more particularly, to electro-mechanical stripline switches mountable to a circuit board.
Switches have long been used in electrical circuit designs to isolate a portion of an electrical circuit. In its simplest form, a switch operates to allow a signal to pass from an input terminal to an output terminal in a “closed” position and to prevent the signal from passing from the input terminal to the output terminal in an “open” position. Other such switches, such as those having a single pole dual throw (SPDT), switch between contacts for different functions.
Micro-electromechanical systems (MEMS) are electro-mechanical devices that generally range in size from a micrometer to a millimeter in a miniature sealed package. In the microwave and mm-wave frequency range, switches are used in instrumentation, communications, radar, fiber optic and many other systems that require high-frequency switching. For example, a switch can be used for pulse modulation, port isolation, transfer switching, high-speed switching, replacement of mechanical parts and other switch applications.
A MEMS device in the form of a microswitch has a movable actuator, sometimes referred to as a movable electrode, that is moved toward a stationary electrical contact by the influence of a gate driver (also referred to as a gate or substrate electrode) positioned on a substrate below the movable actuator. The movable actuator may be a flexible beam that bends under applied forces such as electrostatic attraction, magnetic attraction and repulsion, or thermally induced differential expansion, that closes a gap between a free end of the beam and the stationary contact. If a large enough differential voltage exists between the free end of the beam and the stationary electrical contact, a resulting electrostatic force can cause the beam to self-actuate without any gating signal being provided by a gate driver. In certain current switching applications, this self-actuation can result in catastrophic failure of the switch or downstream systems.
There a number of commercially available high-frequency switches on the market today. Unfortunately, most or all of these switches require trade-offs on performance as they are unable to operate within all desired features simultaneously including obtaining high switch isolation greater than 15 dBm, high power handling above 24 dBm, and low insertion loss of a fraction of a dB from DC to mm-wave frequencies. For example, high-frequency switches employing field-effect transistors (FETs) typically are unable to handle high frequencies in the mm-wave range and/or high power above 24 dBm. In the alternative, FET-based solutions may have high insertion loss. In addition, waveguide-based switches are difficult to integrate and lack the required bandwidth coverage to DC. Furthermore, coupling-based diplexers typically have poor isolation and high insertion loss at the cross-over frequency.
In the field particular to analyzer and scope attenuators, millimeter wave microswitches are desired that are hot-switchable +30 dBm, have a high durability (e.g. rated at 10 million cycles), and are capable of being mountable to a circuit board. However, there is a lack of hot-switchable, small, circuit board mountable switches on the market. Existing millimeter wave switches are large, connectorized assemblies that are not easily gang-assembled to a circuit board. Such existing millimeter switches would be difficult, for instance, to use with a Spectrum Analyzer attenuator with 70 dB of dynamic range where 16 SPDT switches may be required.
Accordingly, the need remains for millimeter wave switches that overcome the drawbacks of the existing art while providing functions useful for today's modern equipment.